1 files changed, 162 insertions, 0 deletions

diff --git a/crates/ra_syntax/src/parsing/lexer/ptr.rs b/crates/ra_syntax/src/parsing/lexer/ptr.rs
new file mode 100644
index 000000000..c341c4176
--- /dev/null
+++ b/crates/ra_syntax/src/parsing/lexer/ptr.rs
@@ -0,0 +1,162 @@
+use crate::TextUnit;
+
+use std::str::Chars;
+
+/// A simple view into the characters of a string.
+pub(crate) struct Ptr<'s> {
+    text: &'s str,
+    len: TextUnit,
+}
+
+impl<'s> Ptr<'s> {
+    /// Creates a new `Ptr` from a string.
+    pub fn new(text: &'s str) -> Ptr<'s> {
+        Ptr { text, len: 0.into() }
+    }
+
+    /// Gets the length of the remaining string.
+    pub fn into_len(self) -> TextUnit {
+        self.len
+    }
+
+    /// Gets the current character, if one exists.
+    pub fn current(&self) -> Option<char> {
+        self.chars().next()
+    }
+
+    /// Gets the nth character from the current.
+    /// For example, 0 will return the current character, 1 will return the next, etc.
+    pub fn nth(&self, n: u32) -> Option<char> {
+        self.chars().nth(n as usize)
+    }
+
+    /// Checks whether the current character is `c`.
+    pub fn at(&self, c: char) -> bool {
+        self.current() == Some(c)
+    }
+
+    /// Checks whether the next characters match `s`.
+    pub fn at_str(&self, s: &str) -> bool {
+        let chars = self.chars();
+        chars.as_str().starts_with(s)
+    }
+
+    /// Checks whether the current character satisfies the predicate `p`.
+    pub fn at_p<P: Fn(char) -> bool>(&self, p: P) -> bool {
+        self.current().map(p) == Some(true)
+    }
+
+    /// Checks whether the nth character satisfies the predicate `p`.
+    pub fn nth_is_p<P: Fn(char) -> bool>(&self, n: u32, p: P) -> bool {
+        self.nth(n).map(p) == Some(true)
+    }
+
+    /// Moves to the next character.
+    pub fn bump(&mut self) -> Option<char> {
+        let ch = self.chars().next()?;
+        self.len += TextUnit::of_char(ch);
+        Some(ch)
+    }
+
+    /// Moves to the next character as long as `pred` is satisfied.
+    pub fn bump_while<F: Fn(char) -> bool>(&mut self, pred: F) {
+        loop {
+            match self.current() {
+                Some(c) if pred(c) => {
+                    self.bump();
+                }
+                _ => return,
+            }
+        }
+    }
+
+    /// Returns the text up to the current point.
+    pub fn current_token_text(&self) -> &str {
+        let len: u32 = self.len.into();
+        &self.text[..len as usize]
+    }
+
+    /// Returns an iterator over the remaining characters.
+    fn chars(&self) -> Chars {
+        let len: u32 = self.len.into();
+        self.text[len as usize..].chars()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_current() {
+        let ptr = Ptr::new("test");
+        assert_eq!(ptr.current(), Some('t'));
+    }
+
+    #[test]
+    fn test_nth() {
+        let ptr = Ptr::new("test");
+        assert_eq!(ptr.nth(0), Some('t'));
+        assert_eq!(ptr.nth(1), Some('e'));
+        assert_eq!(ptr.nth(2), Some('s'));
+        assert_eq!(ptr.nth(3), Some('t'));
+        assert_eq!(ptr.nth(4), None);
+    }
+
+    #[test]
+    fn test_at() {
+        let ptr = Ptr::new("test");
+        assert!(ptr.at('t'));
+        assert!(!ptr.at('a'));
+    }
+
+    #[test]
+    fn test_at_str() {
+        let ptr = Ptr::new("test");
+        assert!(ptr.at_str("t"));
+        assert!(ptr.at_str("te"));
+        assert!(ptr.at_str("test"));
+        assert!(!ptr.at_str("tests"));
+        assert!(!ptr.at_str("rust"));
+    }
+
+    #[test]
+    fn test_at_p() {
+        let ptr = Ptr::new("test");
+        assert!(ptr.at_p(|c| c == 't'));
+        assert!(!ptr.at_p(|c| c == 'e'));
+    }
+
+    #[test]
+    fn test_nth_is_p() {
+        let ptr = Ptr::new("test");
+        assert!(ptr.nth_is_p(0, |c| c == 't'));
+        assert!(!ptr.nth_is_p(1, |c| c == 't'));
+        assert!(ptr.nth_is_p(3, |c| c == 't'));
+        assert!(!ptr.nth_is_p(150, |c| c == 't'));
+    }
+
+    #[test]
+    fn test_bump() {
+        let mut ptr = Ptr::new("test");
+        assert_eq!(ptr.current(), Some('t'));
+        ptr.bump();
+        assert_eq!(ptr.current(), Some('e'));
+        ptr.bump();
+        assert_eq!(ptr.current(), Some('s'));
+        ptr.bump();
+        assert_eq!(ptr.current(), Some('t'));
+        ptr.bump();
+        assert_eq!(ptr.current(), None);
+        ptr.bump();
+        assert_eq!(ptr.current(), None);
+    }
+
+    #[test]
+    fn test_bump_while() {
+        let mut ptr = Ptr::new("test");
+        assert_eq!(ptr.current(), Some('t'));
+        ptr.bump_while(|c| c != 's');
+        assert_eq!(ptr.current(), Some('s'));
+    }
+}